1. Field of the Invention
The present invention essentially relates to an apparatus for real-time tracking--i.e. for detecting, locating and tracking onto--and imaging concretions, within the body of a mammal.
Concretions occur naturally in cavities of mammals, especially human beings. As these concretions form, they rapidly lead to an obstruction of the natural passages, inevitably causing serious physiological disorders that can endanger the life of the mammal concerned.
2. Prior art
In recent years, various devices have been proposed for destroying concretions into small-size fragments that can be evacuated by the natural passages. These devices operate from outside the body using pressure wave generators directed towards the concretion. For example, U.S. Pat. No. 2,559,227 (RIEBER) discloses a pressure wave generator comprising a truncated ellipsoidal reflector in which pressure waves are generated by discharge or an electric arc between two concurrent electrodes at the first focus of the ellipsoid so as to destroy a target, e.g. consisting of a concretion, located at the second focus of the ellipsoid.
In practice, there occurs a serious problem concerning the correct positioning of the target to be destroyed exactly on the second focus of the ellipsoid.
This calls for a detection and exact determination of the position of the target to be destroyed, e.g. a concretion, such as a kidney stone or a biliary concretion.
Various exploratory probes are available for the detection and positioning of such targets, including X-rays or, as is more usually preferred, ultrasounds using ultrasonic transducers.
For example, U.S. Pat. No. 4,444,197 discloses a probe type exploratory apparatus for diagnosis by ultrasound that uses two articulated arms. A similar description is contained in U.S. Pat. No. 4,399,822.
U.S. Pat. No. 4,669,483 discloses a device for spatially positioning an exploratory probe.
The applicants have also proposed a device for spatially positioning an exploratory probe, in copending U.S. patent application Ser. No. 112,434.
However, it turns out in practice that it is necessary for the practitioner to be able to control in real time the position of the concretion and to keep track of its fragmentation during the treatment.
Various solutions have already been put forward for monitoring the position of the concretion and keeping track of its fragmentation during the treatment.
For example, WO-A-8701927 discloses an apparatus for detecting stone fragments, in association with a lithotripter. The lithotriper has a spherical focusing cup serving as a power transducer, and the detection apparatus includes an auxiliary, sectorially-scanned transducer fixed to the center of the cup and connected to an echograph. The apparatus has an auxiliary exciter for the power transducer, generating pulses at a rate of a few hertz and at low power compared with the firing pulses. During the low power pulses, the echograph receiver is operatively connected to an auxiliary cathode-ray tube that produces an A-type echograph image for detecting the stone fragments.
An equivalent disclosure is made in U.S. Pat. No. 4,771,787 and U.S. Pat. No. 4,821,730.
In both devices, the A or B type scanner or transducer is located coaxially to the generator producing pressure waves focused on the target-focus and has to be adjusted on the concretion to be destroyed.
By virtue of the coaxial position of the transducer or A or B type scanner, it is possible to continuously view the concretion when the latter is made to coincide with the focus of the pressure wave generator cup.
However, these devices are limited in their scope for spatial positioning, even if they are mounted so as to revolve around their own axis and to be translatable along the symmetry axis of the pressure wave generator.
Yet the possibility of spatially displacing the concretion locating and imaging apparatus appears necessary in order to keep track of any displacement of the concretion, as well as of the fragments produced in the course of treatment. This is essential to avoid emitting pressure waves that would miss the concretion. The operator should thus be able to stop immediately the emission of pressure waves to proceed to a new locating step.
This is why U.S. Pat. No. 4,663,483 teaches an ultrasonic locating device located at the end of a complex mechanical structure for the spatial detection of the concretion, to determine its coordinates and subsequently to bring the target-focus of the pressure wave generator into coincidence with the concretion to be destroyed, through the use of a complex processing system.
Since the above locating device is somewhat immobilized while the concretion is set into coincidence with the target focus of the pressure wave generator, it cannot be used by the practitioner for real-time observation of the concretion.
This is why it can be noted that the document proposes the inclusion of a complementary real-time imaging device formed by an ultrasonic transducer or scanner fixed to a peripheral point of the pressure wave generator, which can be moved only about the axis of the focusing chamber. This ultrasonic tranducer or scanner has a higher resolution than the displaceable ultrasonic device and allows viewing of the destruction of the concretion (see page 13, lines 6 to 16). Such a limited motion is not sufficient to obtain the best resolution nor monitor wide regions in the body.
Such an auxiliary ultrasound or scanner device has also been proposed in document EP-A-0 265 742. Here, the two ultrasonic locating devices are located at right angles so as to provide viewing planes that are also at right angles. The position of these ultrasonic transducers or scanners is also fixed with respect to the generator.
But, as has already been mentioned above, concretions or their fragments are relatively frequently displaced in the course of a treatment.
This is particularly true for the treatment of biliary concretions. Indeed, these concretions move much more than kidney stones since they have considerably more space within which to move and can easily escape from the target-focus after recoiling from the shock waves, or as a result of patient movements. Furthermore, patients' respiratory movements are considerable at the level of vesicle, given that the vesicle and the liver are both in direct contact with the diaphragm. Thus, there is a strong likelihood in this case that a non-negligible part of the shock or pressure waves does not reach the concretion, owing to the respiratory movements.
All the previously proposed solutions, using a fixed position of the auxiliary ultrasonic locating device or scanner, or using limited axial or two-dimensional displacement relative to the pressure wave generator, have the major drawback of granting little freedom for positioning the locating device making it (in practice) very difficult (if not impossible in at least some instances) to locate and view the concretions effectively in real time, especially in the case of biliary concretions, during the course of the treatments.